generally we were issued with one 50 round mag in the South African Infantry (in mid 80's) and the rest was 35 round mags, the 50 round mag was too long generally - but we carried to back the LMG guys up, in theory when they were changing barrels - or reloading, or clearing a stoppage the idea was we could keep suppressing fire going with the larger capacity mag. Simply though it was impossible to shoot properly in the prone position on on the bipod with the larger mag, mostly I carried 6 x 35 round mags (with 30 in each) as the SADF 5.56 came in 30 round little boxes and then carried a plastic bag with another 300 in my H-frame. We also only loaded the 35 round mags with 30 to stop the spring from being compressed too much over a extended period in your chest webbing, plus you knew it was 30 as you used one little box per mag.